WASHINGTON — U.S. intelligence agencies did not miss a “smoking gun” that could have prevented an alleged attempt to blow up a U.S. airliner on Christmas Day, President Barack Obama”s top counterterrorism adviser said Sunday.

White House aide John Brennan cited “lapses” and errors in the sharing of intelligence and clues about the Nigerian man accused in the foiled attempt.

“There is no smoking gun,” Brennan said. “There was no single piece of intelligence that said, ”this guy is going to get on a plane.””

The Transportation Security Administration announced Sunday that, starting today, passengers flying into the United States from Nigeria, Yemen and other “countries of interest” will be subject to enhanced screening techniques, such as body scans and pat-downs. All passengers on U.S.-bound international flights will be subject to random screening, the agency said.

Umar Farouk Abdulmutallab, the Nigerian student who allegedly tried to set off an explosive device aboard the Northwest airliner, has told U.S. investigators he received training and instructions from al-Qaida operatives in Yemen.

Brennan is leading a White House review of the incident. Obama has said there was a systemic failure to prevent the attack, which he said was instigated by an affiliate in Yemen of the al-Qaida terrorist network.

Obama ordered a thorough look at the shortcomings that permitted the plot, which failed not because of U.S. actions but because the would-be attacker failed to set off a deadly detonation. The president has summoned homeland security officials to meet with him in the White House Situation Room on Tuesday.

Brennan cited “a number of streams of information” — the 23-year-old suspect”s name was known to intelligence officials, his father had passed along his concern about the son”s increasing radicalization — and “little snippets” from intelligence channels. “But there was nothing that brought it all together.”

“In this one instance, the system didn”t work. There were some human errors. There were some lapses. We need to strengthen it. But day in and day out, the successes are there.”

Abdulmutallab apparently assembled an explosive device, including 80 grams of Pentrite, or PETN, in the aircraft toilet of a Detroit-bound Northwest flight, then planned to detonate it with a syringe of chemicals. Passengers and crew subdued the suspect when he tried to set off the explosion. He succeeded only in starting a fire on himself.

“What we need to do as an intelligence community, as a government, is be able to bring those disparate bits and pieces of information together so we prevent Mr. Abdulmutallab from getting on the plane.”

Brennan didn”t say whether anyone is in line to be fired because of the oversights. He stood by Homeland Security Secretary Janet Napolitano, although he acknowledged she has “taken some hits” for saying that the airline security system had worked. It didn”t, and she clarified her remarks to show she meant that the system worked only after the attack was foiled, Brennan said.

He said the situation was not like before the attacks of Sept. 11, 2001, when intelligence agencies failed to share tips and information that might have uncovered the plot.

He said there “were no turf battles” between agencies. “There”s no evidence whatsoever that any agency or department was reluctant to share” information.